This invention relates to photo-detector arrays which are combined with scanning devices to obtain the combined benefits of staring and scanning detection systems, plus additional benefits otherwise unobtainable.
The present subject matter is somewhat related to the subject matter disclosed and claimed in common assignee application Ser. No. 795,988, filed Nov. 6, 1985, now U.S. Pat. No. 4,675,532, and titled "Combined Staring and Scanning Photodetector Sensing System Having both Temporal and Spatial Filtering." That application contains extensive discussion of the advantages of such a combined staring and scanning system, which is there referred to as a "dynamic staring" system.
The operation of any scanning system requires that the successive radiation signals from a given pixel in the viewed scene by converted into an output signal representing that particular pixel. In a line array system, this may be accomplished by a direct, synchronized transfer and conversion of each pixel input signal to a corresponding output signal available to the observer.
This transfer may require integration of successive signals from a given pixel prior to electronic transfer of the pixel output. The common method used for such integration is the use of a semiconductor charge transfer device (CTD) array, such as a charge-coupled device (CCD) array, or a bucket-brigade (BB) array.
CCD arrays may also be used to integrate pixel signals in two-dimensional planar arrays of detectors, such as the system disclosed in U.S. Pat. No. 3,808,435, issued Apr. 30, 1974. That patent deals with the problem of excessive background radiation by "utilization of a quantum differential detector", which "requires a chopper" to generate an a.c. signal. As acknowledged in U.S. Pat. No. 3,808,435: "The chopper can be eliminated when the device is operated as a line scanner. In this mode the signal is proportional to changes in intensity as the scene sweeps across the detector. This mode, though potentially very useful, cannot readily be extended to a two-dimensional imager."
Many of the prior art difficulties in providing adequate photodetector signals from a two-dimensional focal plane have been solved by the "Z-technology" developed by the assignee of this application. The term "Z-technology" refers to the fact that a focal plane module, which has circuit-carrying layers perpendicular to the focal plane, has a depth dimension Z, in addition to the X and Y dimensions of the focal plane.